Firing oven for ceramic material

ABSTRACT

In a vacuum oven for firing such ceramic materials as false teeth, a sealing plate is pneumatically reciprocable into and out of sealing engagement with a bottom opening in a vertical firing chamber of the oven, with a carrier for the ceramic material being mounted on the sealing plate and spaced therefrom to carry the material into the chamber when the sealing plate is moved vertically upwardly. A slow closing movement is made possible by providing an additional, crank driven lifting element programmed to be vertically reciprocable between a first position in detachable engagement with the sealing plate and a second position vertically removed therefrom, in which position the pneumatic downward reciprocation rapidly opens the oven for removal of the fired material.

United States Patent 11 1 1111 3,860,738

Hintenberger Jan. 14, 1975 1 FIRING OVEN FOR CERAMIC MATERIAL 3,641,2502 1972 Hintenberger 13/31 [76] Inventor: Karlmntenbergermogersm 43,655,941 4/1972 Schaum ..219/390 F kf t ran Ur am Mam Germany PrimaryExaminer-Velodymyr Y. Mayewsky 1 1 Flledi 1973 Attorney, Agent, orFirm-Kurt Kelman Appl. No.2 340,719

Related U.S. Application Data Continuation-in-part of Ser. No. 246,642,April 24, 1972, abandoned.

Foreign Application Priority Data Apr. 27, 1971 Germany 2120592References Cited UNITED STATES PATENTS 4/1964 Hintenberger 13/31 4/1969Eicker 13/20 [57] ABSTRACT In a vacuum oven for firing such ceramicmaterials as false teeth, a sealing plate is pneumatically reciprocableinto and out of sealing engagement with a bottom opening in a verticalfiring chamber of the oven, with a carrier for the ceramic materialbeing mounted on the sealing plate and spaced therefrom to carry thematerial into the chamber when the sealing plate is moved verticallyupwardly. A slow closing movement s ma Q b x ranki anaddit on crankdriven lifting element programmed to be vertically reciprocable betweena first position in detachable engagement with the sealing plate and asecond position vertically removed therefrom, in which position thepneumatic downward reciprocation rapidly opens the oven for removal ofthe fired material.

2 Claims, 1 Drawing Figure FIRING OVEN FOR CERAMIC MATERIAL This is acontinuation-in-part of my copen'ding application Ser. No. 246,642,filed Apr. 24, 1972, now abandoned.

The present invention relates to an improvement in an electricallyheated oven for firing ceramic material, particularly in the manufactureof false teeth, wherein the oven comprises a thermally insulated andvacuumtight shell defining a vertical firing chamber therein.

My U.S. Pat. No. 3,641,250, dated Feb. 8, 1972, describes and claims afurnace for firing a ceramic object, which comprises a shell defining achamber therein, the shell having a closed top and a bottom openingconnecting the chamber with the ambient atmosphere, a firing zoneadjacent the closed top, a sealing plate mounted outside the shell inalignment with the chamber opening for pneumatically operable movementinto sealing engagement with the chamber opening, a pneumatic cylinderreceiving compressed air, a piston defining an axial bore affixed to thesealing plate and glidable in the cylinder, the piston being actuatedunder the pressure of the compressed air to move the sealing plate intothe sealing engagement, evacuating means for withdrawing air from thechamber when the opening is sealed, a carrier for the object between thesealing plate and the chamber opening, a piston glidable in the sealingplate piston bore and affixed to the carrier, and a constricted orificein the sealing plate piston for admitting a controlled amount of thecompressed air into the axial bore to move the carrier piston in respectof the sealing plate piston.

In such a furnace, the firing temperature in the firing zone need not belowered each time the firing chamber is charged since the double-actingpistons for the carrier and the sealing plate control the carriermovement so that the object dwells for a certain time in the vacuum zonebefore it enters the firing zone proper.

However, this arrangement has the disadvantage that the pneumatic liftsfor the sealing plate and the carrier make it difficult to lift thesealing plate and the carrier with the ceramic object slowly, i.e., inabout 6 minutes, through a relatively short path, and then to move themdown rapidly into the cooling position after the ceramic object has beenfired in the furnace. Hydraulic means could be used to achieve this butthis would involve relatively complex and correspondingly expensivestructures while being undesirable, due to possible leaks in thehydraulic circuit and the general instrumentation of the apparatus.

It is accordingly an object of the invention to provide an oven of thegenerally indicated type but which automatically assures a slow movementof the ceramic material into the firing chamber while rapidly removingthe fired material therefrom, the fully automatic operation making itpossible for unskilled personnel to operate the oven, the only task ofthe operator being the placing of the ceramic material on the carrierand the removal of the fired material therefrom.

The above object is accomplished in accordance with this invention byproviding an additional, mechanically driven element for the sealingplate, the element being arranged to be vertically reciprocable betweena first or operative position in detachable supporting engagement withthe sealing plate and a second or rest position vertically spacedtherefrom, and programming means for reciprocating the lifting elementbetween these positions.

In this arrangement, the mechanically driven lifting element slowlylifts the sealing plate while in supporting engagement therewith, thelifting stroke raising the object on the carrier, which moves with thesealing plate whereon it is mounted, about mm in about 6 minutes toplace the object at the end of the stroke into the firing zone. Afterfiring has been completed and the lifting element has been moved intothe rest position, the pneumatically operable rod supporting the sealingplate assures a rapid downward movement thereof to avoid excessivefiring of the object. The downward movement of the sealing plate isdampening when it again engages the lifting element in the secondposition thereof, i.e., when the sealing plate comes to rest on thelifting element while being pneumatically lowered.

In the accompanying drawing, the single FIGURE shows a schematic sideview, partly in section, of the firing oven, including a diagrammaticillustration of the controls for automatically operating the oven.

The illustrated firing oven is generally conventional and comprises ashell 22 lined with thermally insulating fire bricks 23 defining avertical firing chamber 24 which is surrounded by an electricalresistance heater 25. As shown, the shell has a closed top and a bottomopening connecting the firing chamber 24 with the atmosphere. A sealingplate 20 is mounted outside the shell in alignment with the chamberopening. Carrier 5 for ceramic materials to be fired is mounted on thesealing plate and spaced therefrom to carry the ceramic material intothe firing chamber when the sealing plate is moved vertically upwardly,the carrier moving in unison with the sealing plate whereon it ismounted.

Relatively rapid vertical reciprocation of the sealing plate into andout of sealing engagement with the firing chamber opening may beeffected by means of a pneumatic cylinder and piston drive, this drivecomprising a cylinder 2 receiving piston 2a for glidable reciprocationtherein, the piston rod 4 extending from the piston to the sealing platewhich is fixed thereto to support the plate for vertical reciprocationupon supply and withdrawal of pressure fluid to and from cylinder 2.

For the slow lifting of the sealing plate into sealing engagement andthe correspondingly slow movement of the carrier with the ceramicmaterial into the firing zone, the invention provides a lifting rod 6which is arranged to be vertically reciprocable between an operativeposition (shown) wherein the upper rod end 6' is in supportingengagement with the sealing plate and a rest position vertically spacedtherefrom, wherein the pneumatic drive may rapidly move the sealingplate 20 and carrier 5 downwardly so as to enable an operator to removethe fired material from the carrier outside the oven. The lifting rod 6is guided within two brackets 2, 2" affixed to cylinder 2.

The lifting rod 6 is mechanically driven, the illustrated mechanicaldrive being a crank drive 12 comprising a connecting rod 21 linked tothe lifting rod 6 and a crank moving in a circular path 12' duringreciprocation of the lifting rod.

As shown, the oven shell 22 is mounted on a control box 26 by means ofsteel columns 26', the abovedescribed controls and the programming meansto be described hereinafter being mounted in the control box.

The oven is operated as follows:

Before a firing cycle begins and with the oven still open, inert gas issupplied to the firing chamber 24 to flood this chamber, the inert gasbeing fed from pressure cylinder 11 through supply conduit 11a which isconnected by a suitable valve means, such as the illus trated tandemsolenoid valves 17 and 16, to branch conduit 11b leading into mainconduit 27 which leads into the firing chamber through the shell walland fire brick lining of the oven. A gas pressure regulator controls thepressure of the inert gas fed into the firing chamber, and a timer ortiming clock 7 is set to control the operation of solenoid valves l6, l7electrically connected to the timer which opens the valves when it isdesired to flood the firing chamber with inert gas. It should beunderstood that the present invention is equally useful in ovens of thistype which are operated without an inert gas supply. I

A second timer or timing clock 3 is provided for control of theevacuation and sealing of the firing chamber. The timer has twooperating switches 3a and 3b for controlling the chamber evacuation andsealing. Switch 3a is electrically connected to the control circuit forpump 1 and switch 3b is electrically connected to the control circuitfor the operation of crank drive 12. Timer 3 controls evacuation of thefiring chamber and slow sealing thereof by operation of the crank drive.Actuation of push button switch 3b starts operation of the crank driveto lift the sealing plate 20 slowly into sealing engagement with theoven opening, the sealing plate being pushed up by lifting rod 6, thecrank reaching and actuating limit switch 8 when the sealing plateengages the oven opening in the highest position of rod Switch 3b isconnected electrically to a servomotor (not shown) for driving thecrank, the connecting rod 21 slowly lifting the rod 6 to push thesealing plate 20 from its lowermost position, when the sealing platerests on'top, or close to the top, of control box 26, to the illustratedsealing engagement with the firing chamher opening of the oven. As thecrank moves in its circular path, it reaches limit switch 8 coincidentwith the sealing engagement of plate 20 with the oven'operat- As shown,the input of vacuum pump 1 is'connected to evacuating conduit la whichis connected to main conduit 27 through solenoid valve '19. Operation ofswitch 8 connected to timers 3 and 7, which are respectively connectedelectrically to valve 19 and valves 16, 17, opens valve 19 after valvesl6, 17 have been closed so that the pump begins evacuation of firingchamber 24 through conduit 27. Simultaneously, the evacuated gaseousfluid is pumped through output conduit 1b which delivers pneumaticpressure fluid into cylinder 2, throttling valves 18 and 14 in conduit1b controlling the flow of the fluid to determine the amount of fluidsupplied to the cylinder. In this manner, the piston 2a is pressedupwardly and keeps plate 20 in sealing engagement with the oven openingwhile the crank continues its movement from switch 8 to limit switch 9during which stage the lifting rod is lowered by the crank drive out ofengagement with the sealing plate. Check valve 15 in conduit lbmaintains the fluid pressure in the cylinder 2 during this stage ofoperation, i.e., the firing period.

Timers 3 and 7 are set so that, about 1 minute before the end of thefiring period, valve 19 is closed and valves l6, 17 are opened so thatevacuation of the firing chamber stops and inert gas is again suppliedthereto. Finally, at the end of the firing period, the timers willoperate limit switch 9 to stop operation of pump 1 and close the inertgas supply valves 16, 17. Pressure fluid will slowly bleed out ofcylinder 2 through throttle valve 14, fluid return through conduit lbbeing prevented by check valve 15, and the sealing plate 20 with thefired object on carrier 5 will descend to begin the cooling period.Meanwhile, the crank continues moving in its circular path from limitswitch 9 to limit switch 13, supporting the sealing plate during itsdescent when the plate has been lowered pneumatically into supportingengagement with end 6' of lifting rod 6. Thus, a relatively slow descentof the sealing plate during the cooling period is assured. When thecrank reaches switch 13, the servomotor for the crank drive is stoppedand the firing cycle is ended. Actuation of push button switch 3binitiates a new cycle.

When it is desired to close the oven rapidly to avoid heat losses, pushbutton switch 3a is actuated while switch 3b remains open and the crankdrive accordingly remains inoperative. A relay (not shown) is interposedin the electrical connection of switch 30 to pump 1 to start the pumpand thus deliver pneumatic fluid to cylinder 2 to move the sealing platerelatively rapidly into closing engagement with the oven opening whilethe oven chamber is partially evacuated. When the vacuum in the chamberhas reached a set degree, it will operate another relay in the controlcircuit for pump 1 so that valve 19 will be closed and the pumpoperation terminated. Thus, the oven will remain closed with a partialvacuum therein during intervals in the firing operation and undue heatlosses from the oven will be avoided.

When it is desired rapidly to open the oven chamber, timer 7 closesvalve 16, the partial vacuum in the oven chamber is reduced and thesealing plate descends, the rapidity of the lowering being controlledbythrottle valvel4.

lclaimz y 1. In an oven for firing ceramic mate,rial', which' comprisesan electrical circuit operable with a pneumatic circuit,.a thermallyinsulated and vacuum-tight electrically heated shell defining ,avertical firing chamber therein, the shell having a closed top and abottom opening connecting the chamber with the ambient atmosphere,a'se'aling plate mountedoutside the. shell in alignment with the chamberopening, a pneumatically operable lifting rod supporting the sealingplate and vertically reciprocable to move the sealing plate into and outof sealing engagement with the chamber opening, evacuating means forwithdrawing air from the firing chamber when the chamber opening hasbeen sealed, and a carrier for the ceramic material mounted on thesealing plate and spaced therefrom to carry the ceramic material intothe chamber when the sealing plate is vertically upwardly moved, theimprovement of an additional, mechanically driven lifting element forthe sealing plate, the additional mechanically driven liftingelementbeing arranged to be vertically reciprocable between a firstposition in detachable engagement with the sealing plate and a secondposition vertically removed therefrom, and programming means forreciprocating the additional mechanically driven lifting element betweensaid positions, said programming means having a crank drive linked tothe additional mechanically driven lifting element.

2. In the oven of claim 1, the crank driven including a crank passingthrough a circular path during reciprocation of the lifting element, andlimit switches mounted in said circular path.

a: v a: a r

1. In an oven for firing ceramic material, which comprises an electricalcircuit operable with a pneumatic circuit, a thermally insulated andvacuum-tight electrically heated shell defining a vertical firingchamber therein, the shell having a closed top and a bottom openingconnecting the chamber with the ambient atmosphere, a sealing platemounted outside the shell in alignment with the chamber opening, apneumatically operable lifting rod supporting the sealing plate andvertically reciprocable to move the sealing plate into and out ofsealing engagement with the chamber opening, evacuating means forwithdrawing air from the firing chamber when the chamber opening hasbeen sealed, and a carrier for the ceramic material mounted on thesealing plate and spaced therefrom to carry the ceramic material intothe chamber when the sealing plate is vertically upwardly moved, theimprovement of an additional, mechanically driven lifting element forthe sealing plate, the additional mechanically driven lifting elementbeing arranged to be vertically reciprocable between a first position indetachable engagement with the sealing plate and a second positionvertically removed therefrom, and programming means for reciprocatingthe additional mechanically driven lifting element between saidpositions, said programming means having a crank drive linked to theadditional mechanically driven lifting element.
 2. In the oven of claim1, the crank driven including a crank passing through a circular pathduring reciprocation of the lifting element, and limit switches mountedin said circular path.